The present invention relates to a device for cooling an engine power unit, and particularly to a cooling device suitable for use for an engine power unit which is provided with a friction type driving force transmission mechanism and which requires compulsory cooling.
Generally, for example, as shown in FIG. 1, an engine power unit 2 mounted on a scooter 1 is covered at its front portion 5 (forward portion in the running direction) or at its outer circumference with a frame cover 3 or the like. As the result, air remains in portions around an engine 4 of the power unit 2 so as to lower the efficiency in cooling the engine 4. Accordingly, means has been provided for compulsorily sending cooling air to the engine 4.
On the other hand, a friction type driving force transmission mechanism is mainly employed as a mechanism for transmitting driving force (for example, a speed change gear) used for the power unit 2 of the above-mentioned scooter 1.
In the case in which the friction type driving force transmission mechanism is employed, however, heat is generated among elements of the mechanism, thereby affecting significantly the efficiency in power transmission or the endurance of the mechanism, so that cooling becomes necessary. The cooling requirement has become more important as engines have become more powerful.
In FIG. 2, a conventional engine cooling system is shown in which a shroud 6 surrounding an engine 4 is provided on one side portion of the engine 4 along the longitudinal direction of a crank-shaft 5. A first exterior air inlet 7 is formed in the shroud 6 at a position opposite to an end of the crank-shaft 5, a first fan 8 for sucking exterior air through the first exterior air inlet 7 being attached at an end of the crank-shaft 5. A driving force transmission mechanism cooling system also is shown in which a belt casing 12 housing a driving force transmission mechanism 11 constituted by a pulley 9 attached on the crank-shaft 5 and a belt 10 hung about the pulley 9 is disposed on a side of the engine 4 opposite the shroud 6. A second exterior air inlet 13 is formed in the belt casing 12 opposite to the pulley 9, a second fan 14 for sucking exterior air into the belt casing 12 through the second exterior air inlet 13 being attached on the pulley 9 on a surface thereof opposite inlet 13.
In this engine cooling system, after the exterior air sucked by the first fan 8 has touched the outer surface of the engine 4 to exchange heat, the air is discharged to the exterior through a gap between the engine 4 and the shroud 6, however, the cooling air flows mainly in the direction shown by arrows in FIG. 2, that is, in the direction opposite to the first fan 8, so that the above-mentioned discharging portions are concentrated near the belt casing 12 and a gas, which has a high temperature after heat exchanged, touches the outer surface of the belt casing 12. As a result, cooling efficiency of the driving force transmission mechanism cooling system may be lowered because the outer surface of the belt casing 12 is heated.